Figure5. Variation in (a) the Peclet number, (b) the Reynolds
number, (c) maximum superficial velocity and (d) minimum fluidization
velocity with time for feed flow rate of 333 kmol/h
The Peclet number quantifies the degree of dispersion introduced into
the system. It is dimensionless so is more convenient than the
dispersion coefficient for this purpose. A high value for the Peclet
number in Figure 5a reveals that an assumption made for ignoring radial
distribution of temperature and concentration is reasonable and the bed
operates under plug flow conditions. Since the adsorption unit is of
horizontal bed type, the Reynolds number is small, as depicted in Figure
5b. Figure 5c and d also indicates that maximum superficial velocity is
kept below the minimum fluidization velocity in horizontal adsorption
unit. According to Figure 5, no significant change in the Peclet number,
Reynolds number and velocities is observed after entrance of adsorption
bed.
Industrial plant operates in a cyclic manner and after conducting
several cycles, the adsorption process approaches to a cyclic steady
state. Determining the required time to reach steady state cyclic
process is typically performed by iteration method. 21Figure 6 gives the simulation results in which cyclic steady state is
established after three sequential running cycles in the process due to
using high regeneration flow rate. Since most of feed (air) is not
adsorbed on adsorbents, only few cycles is required to reach stable
condition and this matter is in good agreement with literature.22Figure 6 shows that unsteady state conditions are
raised due to temperature change and accumulation of energy in the bed.22 The identical component profile is observed after
three cyclic processes in Figure 6a and 6b. Figure 6c shows that
identical temperature is occurred in adsorption bed.